Is it an 5.25 inch or a 3.5 inch ?? My guess it's an 5.25 seeing to options you discribe.
With the 5.25 there are different models around with serveral switches on the back.
I have one with 40 / 80 tracks (switch 3) , and also the D0 D1 (switch 1 and 2).
I never really used it but it might suggest that is for either density HD/DD/SD or
a kind of sided select like SS or DS.
Would have tested it for you but it seems my drives isn't working at the time